// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file. See the AUTHORS file for names of contributors.
 
 #include "util/arena.h"
 
 namespace leveldb {
 
 static const int kBlockSize = 4096;
 
 Arena::Arena() : memory_usage_(0) {
   alloc_ptr_ = nullptr;  // First allocation will allocate a block
   alloc_bytes_remaining_ = 0;
 }
 
 Arena::~Arena() {
   for (size_t i = 0; i < blocks_.size(); i++) {
     delete[] blocks_[i];
   }
 }
 
 char* Arena::AllocateFallback(size_t bytes) {
   if (bytes > kBlockSize / 4) {
     // Object is more than a quarter of our block size.  Allocate it separately
     // to avoid wasting too much space in leftover bytes.
     char* result = AllocateNewBlock(bytes);
     return result;
   }
 
   // We waste the remaining space in the current block.
   alloc_ptr_ = AllocateNewBlock(kBlockSize);
   alloc_bytes_remaining_ = kBlockSize;
 
   char* result = alloc_ptr_;
   alloc_ptr_ += bytes;
   alloc_bytes_remaining_ -= bytes;
   return result;
 }
 
 char* Arena::AllocateAligned(size_t bytes) {
   const int align = (sizeof(void*) > 8) ? sizeof(void*) : 8;
   assert((align & (align-1)) == 0);   // Pointer size should be a power of 2
   size_t current_mod = reinterpret_cast<uintptr_t>(alloc_ptr_) & (align-1);
   size_t slop = (current_mod == 0 ? 0 : align - current_mod);
   size_t needed = bytes + slop;
   char* result;
   if (needed <= alloc_bytes_remaining_) {
     result = alloc_ptr_ + slop;
     alloc_ptr_ += needed;
     alloc_bytes_remaining_ -= needed;
   } else {
     // AllocateFallback always returned aligned memory
     result = AllocateFallback(bytes);
   }
   assert((reinterpret_cast<uintptr_t>(result) & (align-1)) == 0);
   return result;
 }
 
 char* Arena::AllocateNewBlock(size_t block_bytes) {
   char* result = new char[block_bytes];
   blocks_.push_back(result);
   memory_usage_.fetch_add(block_bytes + sizeof(char*),
                           std::memory_order_relaxed);
   return result;
 }
 
 }  // namespace leveldb